Heart disease is the leading cause of death in the United States. A heart attack (also known as an Acute Myocardial Infarction (AMI)) typically results from a thrombus that obstructs blood flow in one or more coronary arteries. AMI is a common and life-threatening complication of coronary heart disease. The sooner that perfusion of the myocardium is restored (e.g., with injection of a thrombolytic medication such as tissue plasminogen activator (tPA)), the better the prognosis and survival of the patient from the heart attack. The extent of damage to the myocardium is strongly dependent upon the length of time prior to restoration of blood flow to the heart muscle.
Fischell et al in U.S. Pat. Nos. 6,112,116, 6,272,379, and 6,609,023 describe implantable systems for detecting the onset of acute myocardial infarction and providing both treatment and alarming to the patient. While Fischell et al discuss the detection of a shift in the S-T segment of the patient's electrogram from an electrode within the heart as the trigger for alarms; it may be desirable to provide more sophisticated detection algorithms to reduce the probability of false positive and false negative detection. In addition while these patents describe some desirable aspects of programming such systems, it may be desirable to provide additional programmability and alarm control features.
In particular, it may be desirable to differentiate the possibly more life threatening occlusion of the Left Anterior Descending (LAD) coronary artery from occlusions of the Circumflex (LCX) or Right Coronary Artery (RCA).
Event detection in the context of a recovery from higher heart rates presents various difficulties. One possibility for handling this problem is described in U.S. patent application Ser. No. 11/710,902 to John et al., filed Feb. 27, 2007, entitled “Systems and methods of medical monitoring according to patient state.” Alternatives to the techniques described in the above mentioned application may prove more suitable for implementation in particular types of cardiac event detection devices.
In the context of body surface electrocardiograms, it is known that ST changes persist after recovery from exercise (i.e. high heart rate). Indeed, the trajectory of the ST vs. heart rate curve after exercise has been proposed as a marker for coronary artery disease. (Okin P M, Ameisen O, Kligfield P. Recovery-phase patterns of ST segment depression in the heart rate domain: identification of coronary artery disease by the rate-recovery loop. Circulation. 1989; 80: 533-541.)
For the purpose of this invention, the term “electrocardiogram” is defined to be the heart electrical signals from one or more skin surface electrode(s) that are placed in a position to indicate the heart's electrical activity (depolarization and repolarization). An electrocardiogram segment refers to the recording of electrocardiogram data for either a specific length of time, such as 10 seconds, or a specific number of heart beats, such as 10 beats. For the purposes of this specification the PQ segment of a patient's electrocardiogram is the typically flat segment of a beat of an electrocardiogram that occurs just before the R wave.
For the purpose of this invention, the term “electrogram” is defined to be the heart electrical signals from one or more implanted electrode(s) that are placed in a position to indicate the heart's electrical activity (depolarization and repolarization). An electrogram segment refers to the recording of electrogram data for either a specific length of time, such as 10 seconds, or a specific number of heart beats, such as 10 beats. For the purposes of this specification the PQ segment of a patient's electrogram is the typically flat segment of an electrogram that occurs just before the R wave. For the purposes of this specification, the terms “detection” and “identification” of a cardiac event have the same meaning. A beat is defined as a sub-segment of an electrogram or electrocardiogram segment containing exactly one R wave.
Heart signal parameters include PQ segment average value, ST segment average voltage value, R wave peak value, ST deviation, ST shift, average signal strength, T wave peak height, T wave average value, T wave deviation, heart rate, R-R interval and peak-to-peak voltage amplitude.